Method for determining precoding matrix indicator, user equipment, and base station evolved nodeb

ABSTRACT

The present disclosure relates to a method for determining a precoding matrix indicator, a user equipment (UE), a base station (e.g., eNB), and a system. The method includes: receiving a reference signal sent by a base station; selecting, based on the reference signal, a precoding matrix from a codebook, where a precoding matrix W included in the codebook is a product of two matrices W 1  and W 2 , where W 1  is a block diagonal matrix, where each block matrix is a Kronecker product of a matrix A i  and a matrix B i ; and sending a precoding matrix indicator (PMI) to the base station, where the PMI corresponds to the selected precoding matrix, so that the base station obtains the precoding matrix according to the PMI.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 16/164,719, filed on Oct. 18, 2018, which is a continuation of U.S. application Ser. No. 15/834,984 filed on Dec. 7, 2017, now U.S. Pat. No. 10,122,427, which is a continuation of U.S. application Ser. No. 14/923,019 filed on Oct. 26, 2015, now U.S. Pat. No. 9,859,962, which is a continuation of U.S. application Ser. No. 14/569,522 filed on Dec. 12, 2014 now U.S. Pat. No. 9,203,491, which is a continuation of International Application No. PCT/CN2012/076898, filed on Jun. 14, 2012. All of the afore-mentioned patent applications are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

The present invention relates to the field of mobile communications, and in particular, to a method for determining a precoding matrix indicator, a user equipment, a base station evolved NodeB, and a system.

BACKGROUND

A multiple-input multiple-output (MIMO) radio system can obtain diversity and array gains by means of transmit precoding and receive signal combination. A system that utilizes precoding may be expressed as:

y=H{circumflex over (V)}s+n

where y represents a vector of a received signal, H represents a channel matrix, {circumflex over (V)} represents a precoding matrix, s represents a vector of a transmitted symbol, and H represents a measurement noise.

Optimal precoding generally requires that channel state information (CSI) is completely known by a transmitter. A commonly used method is that a user equipment (UE) or a mobile station (MS) (hereinafter generally referred to as UE) quantizes instantaneous CSI and feeds back the CSI to a NodeB, which includes a base station (BS), an access point, a transmission point (TP), or an evolved NodeB (eNB), where the evolved NodeB is generally referred to as an eNB. CSI information that is fed back by an existing Long Term Evolution (LTE) R8 system includes information such as a rank indicator (RI), a precoding matrix indicator (PMI), and a channel quality indicator (CQI), where the RI and the PMI respectively indicate the number of layers used and a precoding matrix. A set of used precoding matrices is generally referred to as a codebook, where each precoding matrix is a codeword in the codebook. To reduce system costs and meet higher requirements on the system capacity and coverage, an active antenna system (AAS) is already widely deployed in practice. Compared with an existing base station antenna, the AAS further provides a degree of freedom in design for the vertical direction.

An existing 4-antenna codebook, which is designed based on Householder transformation, of an LTE R8 system and an existing 8-antenna codebook, which is designed based on dual codebooks, of an LTE R10 system are mainly designed for a horizontal antenna, but a degree of freedom of a vertical antenna is not considered. When the 4-antenna codebook and the 8-antenna codebook are directly used in deployment of an AAS base station antenna, system performance severely deteriorates.

SUMMARY

Embodiments of the present invention provide a method for determining a precoding matrix indicator, a user equipment, a base station evolved NodeB eNB, and a system, which use a precoding matrix that supports vertical and horizontal quantization, and can fully use a degree of freedom of an active antenna system in a vertical direction, thereby improving CSI feedback accuracy and system throughput.

According to one aspect, an embodiment of the present invention provides a method for determining a precoding matrix indicator, where the method includes:

receiving a reference signal sent by a base station;

selecting, based on the reference signal, a precoding matrix from a codebook, where a precoding matrix W included in the codebook is a product of two matrices W₁ and W₂, where

W₁ is a block diagonal matrix, that is, W₁=diag{X₁, . . . , X_(N) _(B) }, where each block matrix X_(i) is a Kronecker product of a matrix A_(i) and a matrix B_(i), that is X_(i)=A_(i)⊗B_(i) and 1≤i≤N_(B); and the W₁ includes at least one block matrix, that is, the number of block matrices is N_(B)≥1; and

sending a precoding matrix indicator PMI to the base station, where the PMI corresponds to the selected precoding matrix, so that the base station obtains the precoding matrix according to the PMI.

According to another aspect, an embodiment of the present invention further provides a method for determining a precoding matrix indicator, where the method includes:

sending a reference signal to a user equipment UE; and

receiving a precoding matrix indicator PMI sent by the UE, where the PMI corresponds to a precoding matrix that is selected by the U, based on the reference signal, from a codebook; and a precoding matrix W included in the codebook is a product of two matrices W₁ and W₂, where

W₁ is a block diagonal matrix, that is, W₁=diag{X₁, . . . , X_(N) _(B) }, where each block matrix X_(i) is a Kronecker product of a matrix A_(i) and a matrix B_(i), that is, X_(i)=A_(i)⊗B_(i), and 1≤i≤N_(B); and the matrix W₁ includes at least one block matrix, that is, the number of block matrices is N_(B)≥1.

According to another aspect, correspondingly, an embodiment of the present invention provides a user equipment UE, including:

a receiving unit, configured to receive a reference signal sent by a base station;

a selecting unit, configured to select, based on the reference signal, a precoding matrix from a codebook, where a precoding matrix W included in the codebook is a product of two matrices W₁ and W₂, where

W₁ is a block diagonal matrix, that is, W₁=diag{X₁, . . . , X_(N) _(B) }, where each block matrix X_(i) is a Kronecker product of a matrix A_(i) and a matrix B_(i), that is, X_(i)=A_(i)⊗B_(i), and 1≤i≤N_(B); and the W₁ includes at least one block matrix, that is, the number of block matrices is N_(B)≥1; and

a sending unit, configured to send a precoding matrix indicator PMI to the base station, where the PMI corresponds to the selected precoding matrix, so that the base station obtains the precoding matrix according to the PMI.

According to another aspect, correspondingly, an embodiment of the present invention provides a base station eNB, including:

a sending unit, configured to send a reference signal to a user equipment UE; and

a receiving unit, configured to receive a precoding matrix indicator PMI sent by the UE, where the PMI corresponds to a precoding matrix that is selected by the UE, based on the reference signal, from a codebook; and a precoding matrix W included in the codebook is a product of two matrices W₁ and W₂, where

W₁ is a block diagonal matrix, that is, W₁=diag{X₁, . . . , X_(N) _(B) }, where each block matrix X_(i) is a Kronecker product of a matrix A_(i) and a matrix B_(i), that is, X_(i)=A_(i)⊗B_(i), and 1≤i≤N_(B); and the matrix W₁ includes at least one block matrix, that is, the number of block matrices is N_(B)≥1.

According to another aspect, correspondingly, an embodiment of the present invention further provides a system for determining a precoding matrix indicator, including the foregoing terminal UE and base station eNB.

The method for determining a precoding matrix indicator, the user equipment UE, the base station eNB, and the system according to the embodiments of the present invention utilize a precoding matrix that supports vertical and horizontal quantization, which can not only use a degree of freedom in a horizontal direction, but also can use a degree of freedom in a vertical direction, thereby greatly improving CSI feedback accuracy and system throughput.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a first embodiment of a method for determining a precoding matrix indicator according to the present invention;

FIG. 2 is a flowchart of a second embodiment of a method for determining a precoding matrix indicator according to the present invention;

FIG. 3 is a schematic structural diagram of composition of a system for determining a precoding matrix indicator according to the present invention;

FIG. 4 is a schematic structural diagram of composition of a user equipment UE in FIG. 3; and

FIG. 5 is a schematic structural diagram of composition of a base station eNB in FIG. 3.

DETAILED DESCRIPTION

The following further describes the technical solutions of the present invention in detail with reference to the accompanying drawings and embodiments.

According to embodiments of the present invention, a codebook scheme is designed for an actual network deployment and antenna configuration, and especially for a base station antenna configuration condition of an active antenna system. According to the codebook scheme, a UE selects and reports a PMI, and a NodeB performs precoding according to PMI information reported by the UE, so as to improve performance of a system with the foregoing antenna configuration and especially with the AAS base station antenna configuration. The base station antenna can not only use a degree of freedom in a horizontal direction, but also can use a degree of freedom in a vertical direction.

FIG. 1 is a flowchart of a first embodiment of a method for determining a precoding matrix indicator according to the present invention. As shown in the figure, this embodiment specifically includes the following steps:

Step 101: Receive a reference signal sent by a base station.

Specifically, the reference signal sent by the base station may include a channel state information reference signal (CSI RS), a demodulation reference signal (demodulation RS, DM RS), or a cell-specific reference signal (cell-specific RS, CRS). A user equipment UE may obtain a resource configuration of the reference signal by receiving a notification (for example, RRC (Radio Resource Control) signaling or downlink control information DCI) from an eNB or based on a cell identity ID, and obtain the reference signal from a corresponding resource or subframe.

Step 102: Select, based on the reference signal, a precoding matrix from a codebook, where a precoding matrix W included in the codebook is a product of two matrices W₁ and W₂, that is:

W=W ₁ W ₂  (1)

where W₁ is a block diagonal matrix, that is:

W ₁=diag{X ₁ . . . ,X _(N) _(B) }  (2)

where each block matrix X_(i) is a Kronecker product of a matrix A_(i) and a matrix B_(i), that is:

X _(i) =A _(i) ⊗B _(i),1≤i≤N _(B)  (3)

the W₁ includes at least one block matrix, that is, the number N_(B) of block matrices is:

N _(B)≥1  (4)

Specifically, each column of the matrix A_(i) or of the matrix B_(i) in formula (3) may be a discrete Fourier transform (DFT) vector or may be a column vector of a Hadamard matrix, that is:

A _(i)=[a ₀ a ₁ . . . a _(N) _(a) ⁻¹]  (5)

B _(i)=[b ₀ b ₁ . . . b _(N) _(b) ⁻¹]  (6)

therefore:

a _(k) ∈{f ₀ ,f ₁ , . . . ,f _(N) _(f) ⁻¹ },k=0, . . . ,N _(a)−1  (7)

or

a _(k) ∈{h ₀ ,h ₁ , . . . ,h _(N) _(h) ⁻¹ },k=0, . . . ,N _(a)−1  (8)

or

b _(l) ∈{f ₀ ,f ₁ , . . . ,f _(N) _(f) ⁻¹ },l=0, . . . ,N _(b)−1  (9)

or

b _(l) ∈{h ₀ ,h ₁ , . . . ,h _(N) _(h) ⁻¹ },l=0, . . . ,N _(b)−1  (10)

where N_(a) and N_(b) represent the numbers of columns of the matrix A_(i) and the matrix B_(i), respectively; h_(m), m=0, . . . , N_(h)−1 represents a column vector of the Hadamard matrix, where N_(h) represents the number of columns of the Hadamard matrix; and f_(n)=0, . . . , N_(f)−1 represents a DFT vector, where N_(f) is the number of DFT vectors, and the DFT vector f_(n) may be represented as:

$\begin{matrix} {f_{n} = \left\lbrack {e^{j\frac{2{\pi \cdot 0 \cdot n}}{N}}\mspace{14mu} e^{j\frac{2{\pi \cdot 1 \cdot n}}{N}}\mspace{14mu} \cdots \mspace{14mu} e^{j\frac{2{\pi \cdot {({M - 1})} \cdot n}}{N}}} \right\rbrack^{T}} & (11) \end{matrix}$

where both M and N are integers.

Specifically, the matrix A_(i) or the matrix B_(i) in formula (3) may also be a precoding matrix in a 2-antenna codebook or a 4-antenna codebook of an LTE R8 system, or in an 8-antenna codebook of an LTE R10 system.

Further, the matrix W₂ is used to select or weight and combine a column vector in the matrix W₁, so as to form the matrix W.

In an example in which the number of block matrices is N_(B)=2 and there are 32 transmit antennas, matrices that form the precoding matrix W may separately be:

A _(i) =a ₀ ,i=1,2  (12)

where:

a ₀ ∈{f ₀ ,f ₁ , . . . ,f ₃}  (13)

[f ₀ ,f ₁ ,f ₂ ,f ₃]=diag{1,e ^(jnπ/8) ,e ^(jnπ/4) ,e ^(jnπ/8) }F ₄ ,n=0,1,2,3  (14)

$\begin{matrix} {{F_{4} = {\frac{1}{2} \times \begin{bmatrix} 1 & 1 & 1 & 1 \\ 1 & j & {- 1} & {- j} \\ 1 & {- 1} & 1 & {- 1} \\ 1 & {- j} & {- 1} & j \end{bmatrix}}}{or}} & (15) \\ {{a_{k} \in \left\{ {h_{0},h_{1},\ldots \;,h_{3}} \right\}},{k = 0},\ldots \;,3} & (16) \\ {\left\lbrack {h_{0},h_{1},\ldots \;,h_{3}} \right\rbrack = {\frac{1}{2} \times H_{4}}} & (17) \end{matrix}$

where H₄ is a Hadamard matrix of order 4.

$\begin{matrix} {{B_{i} \in \left\{ {{{\left\lbrack {b_{{({2k})}{mod}\; 32}\mspace{14mu} b_{{({{2k} + 1})}{mod}\; 32}\mspace{14mu} b_{{({{2k} + 2})}{mod}\; 32}\mspace{14mu} b_{{({{2k} + 3})}{mod}\; 32}} \right\rbrack \text{:}k} = 0},1,\cdots \;,15} \right\}},{i = 1},2} & (18) \\ {{b_{{({{2k} + l})}{mod}\; 32} = \left\lbrack {e^{j\frac{2{\pi \cdot 0 \cdot {({{({{2k} + l})}{mod}\; 32})}}}{32}}\mspace{14mu} e^{j\frac{2{\pi \cdot 1 \cdot {({{({{2k} + l})}{mod}\; 32})}}}{32}}\mspace{14mu} e^{j\frac{2{\pi \cdot 2 \cdot {({{2k} + l})}}{mod}\; 32}{32}}\mspace{14mu} e^{j\frac{2{\pi \cdot 3 \cdot {({{({{2k} + l})}{mod}\; 32})}}}{32}}} \right\rbrack^{T}},{l = 0},1,2,3} & (19) \end{matrix}$

where x mod y represents an operation of x mod y; and j represents a unit pure imaginary number, that is, j=√{square root over (−1)}; or

B_(i) is a precoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

$\begin{matrix} {\mspace{76mu} {W_{2} \in \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix} Y \\ Y \end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix} Y \\ {jY} \end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix} Y \\ {- Y} \end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix} Y \\ {- {jY}} \end{bmatrix}}} \right\}}} & (20) \\ {\mspace{76mu} {{Y \in \left\{ {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{3},{\overset{\sim}{e}}_{4}} \right\}}\mspace{76mu} {or}}} & (21) \\ {\mspace{76mu} {W_{2} \in \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix} Y_{1} & Y_{2} \\ Y_{1} & {- Y_{2}} \end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix} Y_{1} & Y_{2} \\ {jY}_{1} & {- {jY}_{2}} \end{bmatrix}}} \right\}}} & (22) \\ {\left( {Y_{1},Y_{2}} \right) \in \left\{ {\left( {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{1}} \right),\left( {{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{2}} \right),\left( {{\overset{\sim}{e}}_{3},{\overset{\sim}{e}}_{3}} \right),\left( {{\overset{\sim}{e}}_{4},{\overset{\sim}{e}}_{4}} \right),\left( {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{2}} \right),\left( {{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{3}} \right),\left( {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{4}} \right),\left( {{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{4}} \right)} \right\}} & (23) \end{matrix}$

where {tilde over (e)}_(n), n=1,2,3,4 represents a 4×1 selection vector in which all elements are 0 except the n^(th) element being 1.

In an example in which the number of block matrices is N_(B)=2 and there are 32 transmit antennas, matrices that form the precoding matrix W may also separately be:

A _(i)=[a ₀ a _(l)],i=1,2  (24)

a ₀ ,a ₁ ∈{f ₀ ,f ₁ , . . . f ₃}  (25)

where f_(i), i=0, . . . , 3 is shown in formula (14).

or

a ₀ ,a ₁ ∈{h ₀ ,h ₁ , . . . ,h ₃}  (26)

where h_(i), i=0, . . . , 3 is shown in formula (17);

the matrix B_(i), i=1,2 is shown in formulas (18) and (19), or the matrix B_(i) is a precoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system;

$\begin{matrix} {\mspace{76mu} {W_{2} \in \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix} Y \\ Y \end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix} Y \\ {jY} \end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix} Y \\ {- Y} \end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix} Y \\ {- {jY}} \end{bmatrix}}} \right\}}} & (27) \\ {\mspace{76mu} {{Y \in \left\{ {e_{1},e_{2},e_{3},e_{4},e_{5},e_{6},e_{7},e_{8}} \right\}}\mspace{76mu} {or}}} & (28) \\ {\mspace{76mu} {W_{2} \in \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix} Y_{1} & Y_{2} \\ Y_{1} & {- Y_{2}} \end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix} Y_{1} & Y_{2} \\ {jY}_{1} & {- {jY}_{2}} \end{bmatrix}}} \right\}}} & (29) \\ {\left( {Y_{1},Y_{2}} \right) \in \left\{ {\left( {e_{1},e_{1}} \right),\left( {e_{2},e_{2}} \right),\left( {e_{3},e_{3}} \right),\left( {e_{4},e_{4}} \right),\left( {e_{1},e_{2}} \right),\left( {e_{2},e_{3}} \right),\left( {e_{1},e_{4}} \right),\left( {e_{2},e_{4}} \right)} \right\}} & (30) \end{matrix}$

where e_(n), n=1, 2, . . . , 8 represents an 8×1 selection vector in which all elements are 0 except the n^(th) element being 1.

Specifically, the selecting, based on the reference signal, a precoding matrix from a codebook includes:

obtaining, by the user equipment UE based on the reference signal, a channel estimate; and selecting, based on a predefined criterion such as a channel capacity or throughput maximization criterion, the precoding matrix from the codebook according to the channel estimate. Selecting, based on a predefined criterion, a precoding matrix is an existing technology, and details are not described herein.

Further, the selecting, based on the reference signal, a precoding matrix from a codebook includes:

selecting, based on the reference signal, the precoding matrix from a codebook subset, where

the codebook subset may be a codebook subset that is predefined; or a codebook subset that is reported by the UE to the base station eNB, determined by the base station eNB based on the report from the UE, and notified to the UE; or a codebook subset that is determined and reported by the UE, for example, a latest reported codebook subset.

Further, the codebook subset may include:

a subset of the matrix W₁, the matrix A_(i), the matrix B_(i), or the matrix W₂.

The selecting, based on the codebook subset, the precoding matrix can further reduce feedback overheads and implementation complexity.

Further, the codebook subsets have a same subset of the matrix W₁ the matrix A_(i), the matrix B_(i), or the matrix W₂. In this way, the codebook subsets overlap each other, which can overcome an edge effect of channel state information quantization.

Further, in the precoding matrix, block matrices X_(i) and X_(j), i≈j may be unequal, or may also be equal. If there are multiple cases that X_(i) and X_(j), i≈j are equal, for example, X_(i) and X_(j), i≈j that are equal may appear in pairs, the feedback overheads can be further reduced.

In addition, the foregoing matrix A_(i) or matrix B_(i) may also use another form, which is not further elaborated herein.

It should be noted that, each of the foregoing matrices may further be multiplied by a scale factor, so as to implement power normalization or power equalization.

Step 103: Send a precoding matrix indicator PMI to the base station, where the PMI corresponds to the selected precoding matrix, so that the base station obtains the precoding matrix according to the PMI.

Specifically, the precoding matrix is included in a precoding matrix set or a codebook; and the PMI is used to indicate the selected precoding matrix in the precoding matrix set or the codebook.

Specifically, sending a precoding matrix indicator PMI to the base station includes: sending the precoding matrix indicator PMI to the base station, where the PMI may include only one specific value. In this case, the PMI directly indicates the precoding matrix W. For example, if there are a total of 16 different precoding matrices, PMI=0, . . . , 15 may be used to respectively indicate precoding matrices W whose labels are 0, 1, . . . , 15.

Specifically, sending a precoding matrix indicator PMI to the base station may also include: sending precoding matrix indicators PMI₁ and PMI₂ to the base station, where PMI₁ and PMI₂ are used to indicate the matrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B) in formula (2) and the matrix W₂, respectively; and in this case, the matrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B) and the matrix W₂ are respectively indicated by PMI₁ and PMI₂ in the codebook; or

sending precoding matrix indicators PMI₁₁, PMI₁₂, and PMI₂ to the base station, where PMI₁₁, PMI₁₂, and PMI₂ are used to indicate the matrix A_(i), 1≤i≤N_(B), the matrix B_(i), 1≤i≤N_(B), and the matrix W₂, respectively; and in this case, the matrix A_(i), 1≤i≤N_(B), the matrix B_(i), 1≤i≤N_(B), and the matrix W₂ are respectively indicated by PMI₁₁, PMI₁₂, and PMI₂ in the codebook.

Further, the precoding matrix indicators PMI₁ and PMI₂, or the precoding matrix indicators PMI₁₁, PMI₁₂, and PMI₂ have different time domain granularities or frequency domain granularities, for example, PMI₁ and PMI₂, or PMI₁₁, PMI₁₂, and PMI₂ separately indicate different periods or bandwidth channel features, or are obtained based on different subframe periods or subband sizes.

Alternatively, further, the precoding matrix indicators PMI₁₁ and PMI₁₂ are sent to the base station according to different time periods.

Specifically, sending a precoding matrix indicator PMI to the base station may also include: sending precoding matrix indicators PMI_(1,i), 1≤i≤N_(B); and PMI₂ to the base station, where PMI_(1,i), 1≤i≤N_(B) and PMI₂ are used to indicate the matrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B) and the matrix W₂, respectively; or

sending precoding matrix indicators PMI_(11,i), PMI_(12,i) and PMI₂ to the base station, where PMI_(11,i), PMI_(12,i), and PMI₂ are used to indicate the matrix A_(i), 1≤i≤N_(B), the matrix B_(i), 1≤i≤N_(B), and the matrix W₂, respectively.

Specifically, sending a precoding matrix indicator PMI to the base station may also include: sending precoding matrix indicators PMI_(1,i), 1≤i≤N_(B)/2 and PMI₂ to the base station, where PMI_(1,i), 1≤i≤N_(B)/2 and PMI₂ are used to indicate a matrix X_(2i−1)=X_(2i)=A_(2i)⊗B_(2i), 1≤i≤N_(B)/2 and the matrix W₂, respectively; and in this case, X_(2i−1)=X_(2i), and the matrices appear in pairs; or

sending precoding matrix indicators PMI_(11,i), PMI_(12,i), and PMI₂ to the base station, where PMI_(11,i), PMI_(12,i), and PMI₂ are used to indicate a matrix A_(2i−1)=A_(2i), 1≤i≤N_(B)/2 the matrix B_(2i−1)=B_(2i), 1≤i≤N_(B)/2, and the matrix W₂, respectively; and in this case, A_(2i−1)=A_(2i), B_(2i−1)=B_(2i), and the matrices appear in pairs.

Specifically, sending a precoding matrix indicator PMI to the base station may be sending, by the U, the precoding matrix indicator PMI to the base station through a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH).

Further, sending a precoding matrix indicator PMI to the base station may be separately sending, by the UE by using different subframes or according to different periods, the foregoing PMI₁ and PMI₂; or PMI₁₁, PMI₁₂, and PMI₂; or PMI_(1,i), 1≤i≤N_(B), and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B), and PMI₂; or PMI_(1,i), 1≤i≤N_(B)/2, and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B)/2 and PMI₂ to the base station.

Further, sending a precoding matrix indicator PMI to the base station may also be separately sending, by the UE for different subbands or subband sizes in a frequency domain, the foregoing PMI₁ and PMI₂; or PMI₁₁, PMI₁₂, and PMI₂; or PMI_(1,i), 1≤i≤N_(B), and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B), and PMI₂; or PMI_(1,i), 1≤i≤N_(B)/2, and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B)/2 and PMI₂ to the base station.

In this embodiment of the present invention, a user equipment determines and sends a precoding matrix indicator PMI, where the PMI indicates a precoding matrix. The precoding matrix has a structure of W=W₁W₂, where W₁ is a block diagonal matrix in which each block matrix on a diagonal line is X_(i)=A_(i)⊗B_(i), and i=1, . . . , N_(B), where the matrix A_(i) or the matrix B_(i) effectively supports channel state information quantization in a horizontal direction or a vertical direction, respectively. This can fully use a degree of freedom of an active antenna system AAS in a horizontal direction and a vertical direction, thereby greatly improving channel state information feedback accuracy. In addition, multiple block matrices X_(i) may separately correspond to antenna groups of different polarizations or at different locations, so that the foregoing precoding matrix matches multiple antenna deployments or configurations. The foregoing codebook structure greatly improves performance of MIMO, and especially that of MU-MIMO. Moreover, one or more PMIs are fed back based on a subset to indicate a precoding matrix, which fully uses time/frequency domain/spatial correlation of a channel, thereby greatly reducing feedback overheads.

FIG. 2 is a flowchart of a second embodiment of a method for determining a precoding matrix indicator according to the present invention. As shown in the figure, this embodiment specifically includes:

Step 201: Send a reference signal to a user equipment U.

Specifically, the reference signal may include a channel state information reference signal (CSI RS), a demodulation reference signal (demodulation RS, DM RS), or a cell-specific reference signal (cell-specific RS, CRS). Abase station eNB may notify the user equipment UE of a resource configuration of the reference signal by using RRC (Radio Resource Control) signaling or downlink control information DCI), and instruct the UE to obtain the reference signal from a corresponding resource or subframe. The user equipment UE may also implicitly obtain, based on other information such as a cell identity ID, the resource configuration of the reference signal, and obtain the reference signal from the corresponding resource or subframe.

Step 202: Receive a precoding matrix indicator PMI sent by the user equipment UE, where the PMI corresponds to a precoding matrix selected by the user equipment, based on the reference signal, from a codebook; and a precoding matrix W included in the codebook is a product of two matrices W₁ and W₂, and the precoding matrix has a structure shown in formulas (1) to (4).

Specifically, each column of the matrix A_(i) or of the matrix B_(i) may be a DFT vector or is a column vector of a Hadamard matrix, as shown in formulas (5) to (11); or

specifically, the matrix A_(i) or the matrix B_(i) may also be a precoding matrix in a 2-antenna codebook or a 4-antenna codebook of an LTE R8 system, or in an 8-antenna codebook of an LTE R10 system.

Further, the matrix W₂ is used to select or weight and combine a column vector in the matrix W₁, so as to form the matrix W.

In an example in which the number of block matrices is N_(B)=2 and there are 32 transmit antennas, matrices that form the precoding matrix W may separately be those shown in formulas (12) to (23); or B_(i) is a precoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

In an example in which the number of block matrices is N_(B)=2 and there are 32 transmit antennas, matrices that form the precoding matrix W may separately be those shown in formulas (24) to (30); or B_(i) is a precoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

Specifically, selecting, based on the reference signal, a precoding matrix from a codebook includes:

selecting, based on the reference signal, the precoding matrix from a codebook subset, where

the codebook subset may be a codebook subset that is predefined; or a codebook subset that is reported by the UE to the base station eNB, determined by the base station eNB based on the report from the UE, and notified to the UE; or a codebook subset that is determined and reported by the UE, for example, a latest reported codebook subset.

Further, the codebook subset may include a subset of the matrix W₁, the matrix A_(i), the matrix B_(i), or the matrix W₂.

Further, the codebook subsets have a same subset of the matrix W₁, the matrix A_(i), the matrix B_(i), or the matrix W₂. In this way, the codebook subsets overlap each other, which can overcome an edge effect of channel state information quantization.

Further, in the precoding matrix, block matrices X_(i) and X_(j), i≈j may be unequal, or may also be equal. If there are multiple cases that X_(i) and X_(j), i≈j are equal, for example, X_(i) and X_(j), i≈j that are equal may appear in pairs, feedback overheads can be further reduced.

In addition, the foregoing matrix A_(i) or matrix B_(i) may also use another form, which is not further elaborated herein.

It should be noted that, each of the foregoing matrices may further be multiplied by a scale factor, so as to implement power normalization or power equalization.

Specifically, the precoding matrix is included in a precoding matrix set or a codebook; and the PMI is used to indicate the selected precoding matrix in the precoding matrix set or the codebook.

Specifically, receiving a precoding matrix indicator PMI sent by the user equipment UE includes: receiving the precoding matrix indicator PMI sent by the user equipment UL, where the PMI may include only one specific value. In this case, the PMI directly indicates the precoding matrix W. For example, if there are a total of 16 different precoding matrices, PMI=0, . . . , 15 may be used to respectively indicate precoding matrices W whose labels are 0, 1 . . . 15.

Specifically, receiving a precoding matrix indicator PMI sent by the user equipment UE may also include: receiving precoding matrix indicators PMI₁ and PMI₂ sent by the user equipment UE, where PMI₁ and PMI₂ are used to indicate the matrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B), in formula (2) and the matrix W₂, respectively; and in this case, the matrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B), and the matrix W₂ are respectively indicated by PMI₁ and PMI₂ in the codebook; or

receiving precoding matrix indicators PMI₁₁, PMI₁₂, and PMI₂ sent by the user equipment UE, where PMI₁₁, PMI₁₂, and PMI₂ are used to indicate the matrix A_(i), 1≤i≤N_(B), the matrix B_(i), 1≤i≤N_(B), and the matrix W₂, respectively; and in this case, the matrix A_(i), 1≤i≤N_(B), the matrix B_(i), 1≤i≤N_(B), and the matrix W₂ are respectively indicated by PMI₁₁, PMI₁₂, and PMI₂ in the codebook.

Further, the precoding matrix indicators PMI₁ and PMI₂, or the precoding matrix indicators PMI₁₁, PMI₁₂, and PMI₂ have different time domain granularities or frequency domain granularities, for example, PMI₁ and PMI₂, or PMI₁₁, PMI₁₂, and PMI₂ separately indicate different periods or bandwidth channel features, or are obtained based on different subframe periods or subband sizes.

Alternatively, further, the precoding matrix indicators PMI₁₁ and PMI₁₂ are sent to the base station according to different time periods.

Specifically, receiving a precoding matrix indicator PMI sent by the user equipment UE may also include: receiving precoding matrix indicators PMI_(1,i), 1≤i≤N_(B), and PMI₂ sent by the user equipment UE, where PMI_(1,i), 1≤i≤N_(B) and PMI₂ are used to indicate the matrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B), and the matrix W₂, respectively; or

receiving precoding matrix indicators PMI_(11,i), PMI_(12,i), and PMI₂ sent by the user equipment UE, where PMI_(11,i), PMI_(12,i), and PMI₂ are used to indicate the matrix A_(i), 1≤i≤N_(B), the matrix B_(i), 1≤i≤N_(B), and the matrix W₂ respectively; or

receiving precoding matrix indicators PMI_(1,i), 1≤i≤N_(B)/2, and PMI₂ sent by the user equipment UE, where PMI_(1,i), 1≤i≤N_(B)/2 and PMI₂ are used to indicate a matrix X_(2i−1)=X_(2i)=A_(2i)⊗B_(2i), 1≤i≤N/2, and the matrix W₂ respectively; and in this case, X_(2i−1)=X_(2i), and the matrices appear in pairs; or

receiving precoding matrix indicators PMI_(11,i), PMI_(12,i), and PMI₂ sent by the user equipment UE, where PMI₁₁, PMI_(12,i), and PMI₂ are used to indicate a matrix A_(2i−1)=A_(2i), 1≤i≤N_(B)/2, the matrix B_(2i−1)=B_(2i), 1≤i≤N_(B)/2, and the matrix W₂, respectively; and in this case, A_(2i−1)=A_(2i), B_(2i−1)=B_(2i), and the matrices appear in pairs.

Specifically, receiving a precoding matrix indicator PMI sent by the user equipment UE may be receiving, through a physical uplink control channel (PUCCI) or a physical uplink shared channel (PUSCH), the precoding matrix indicator PMI sent by the user equipment UE.

Further, receiving a precoding matrix indicator PMI sent by the user equipment UE may be separately receiving, by the base station by using different subframes or according to different periods, the foregoing PMI₁ and PMI₂; or PMI₁₁, PMI₁₂, and PMI₂; or PMI_(1,i), 1≤i≤N_(B) and PMI₂ or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B), and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B)/2, and PMI₂ that are sent by the user equipment UE; or

may also be receiving the foregoing PMI₁ and PMI₂; or PMI₁₁, PMI₁₂, and PMI₂; or PMI_(1,i), 1≤i≤N_(B) and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B), and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B)/2, and PMI₂ that are sent for different subbands or subband sizes in a frequency domain by the user equipment U.

In this embodiment of the present invention, a base station eNB receives a precoding matrix indicator PMI sent by a user equipment UE, where the PMI indicates a precoding matrix. The precoding matrix has a structure of W=W₁W₂, where W₁ is a block diagonal matrix in which each block matrix on a diagonal line is X_(i)=A_(i)⊗B_(i), and i=1, . . . , N_(B), where the matrix A_(i) or the matrix B_(i) effectively supports channel state information quantization in a horizontal direction or a vertical direction, respectively. This can fully use a degree of freedom of an active antenna system AAS in a horizontal direction and a vertical direction, thereby greatly improving channel state information feedback accuracy. In addition, multiple block matrices X_(i) may separately correspond to antenna groups of different polarizations or at different locations, so that the foregoing precoding matrix matches multiple antenna deployments or configurations. The foregoing codebook structure greatly improves performance of MIMO, and especially that of MU-MIMO. Moreover, one or more PMIs are fed back based on a subset to indicate a precoding matrix, which fully uses time/frequency domain/spatial correlation of a channel, thereby greatly reducing feedback overheads.

The following describes a system for determining a precoding matrix indicator, a user equipment UE, and a base station eNB in the present invention in detail.

FIG. 3 is a schematic structural diagram of composition of an embodiment of a system for determining a precoding matrix indicator according to the present invention. The system according to this embodiment of the present invention includes a user equipment UE 11 and a base station eNB 12. For a structure of the user equipment UE 11, refer to FIG. 4; and for a schematic structural diagram of the base station eNB 12, refer to FIG. 5.

FIG. 4 is a schematic diagram of a user equipment UE 11 for determining a precoding matrix indicator according to an embodiment of the present invention. As shown in the figure, the user equipment UE 11 includes: a receiving unit 111, a selecting unit 112, and a sending unit 113.

The receiving unit 111 is configured to receive a reference signal sent by a base station.

Specifically, the reference signal sent by the base station may include a channel state information reference signal (CSI RS), a demodulation reference signal (demodulation RS, DM RS), or a cell-specific reference signal (cell-specific RS, CRS). The user equipment UE may obtain a resource configuration of the reference signal by receiving a notification (for example, RRC (Radio Resource Control) signaling or downlink control information DCI) from an eNB or based on a cell identity ID, and obtain the reference signal from a corresponding resource or subframe.

The selecting unit 112 is configured to select, based on the reference signal, a precoding matrix from a codebook, where a precoding matrix W included in the codebook is a product of two matrices W₁ and W₂; and the precoding matrix has the structure shown in formulas (1) to (4).

Specifically, each column of the matrix A_(i) or of the matrix B_(i) may be a DFT vector or may be a column vector of a Hadamard matrix, as shown in formulas (5) to (11); or

specifically, the matrix A_(i) or the matrix B_(i) may also be a precoding matrix in a 2-antenna codebook or a 4-antenna codebook of an LTE R8 system, or in an 8-antenna codebook of an LTE R10 system.

Further, the matrix W₂ is used to select or weight and combine a column vector in the matrix W₁, so as to form the matrix W.

In an example in which the number of block matrices is N_(B)=2 and there are 32 transmit antennas, matrices that form the precoding matrix W may separately be those shown in formulas (12) to (23); or B_(i) is a precoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

In an example in which the number of block matrices is A=2 and there are 32 transmit antennas, matrices that form the precoding matrix W may separately be those shown in formulas (24) to (30); or B_(i) is a precoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

Specifically, selecting, based on the reference signal, a precoding matrix from a codebook includes:

obtaining, by the user equipment UE based on the reference signal, a channel estimate and selecting, based on a predefined criterion such as a channel capacity or throughput maximization criterion, the precoding matrix from the codebook according to the channel estimate. Selecting, based on a predefined criterion, a precoding matrix is an existing technology, and details are not described herein.

Further, selecting, based on the reference signal, a precoding matrix from a codebook includes:

selecting, based on the reference signal, the precoding matrix from a codebook subset, where

the codebook subset may be a codebook subset that is predefined; or a codebook subset that is reported by the UE to the base station eNB, determined by the base station eNB based on the report from the UE, and notified to the UE; or a codebook subset that is determined and reported by the UE, for example, a latest reported codebook subset.

Further, the codebook subset may include a subset of the matrix W₁ the matrix A_(i), the matrix B_(i), or the matrix W₂.

Selecting, based on the codebook subset, the precoding matrix can further reduce feedback overheads and implementation complexity.

Further, the codebook subsets have a same subset of the matrix W₁, the matrix A_(i), the matrix B_(i), or the matrix W₂. In this way, the codebook subsets overlap each other, which can overcome an edge effect of channel state information quantization.

Further, in the precoding matrix, block matrices X_(i) and X_(j), i≈j may be unequal, or may also be equal. If there are multiple cases that X_(i) and X_(j), i≈j are equal, for example, X_(i) and X_(j), i≈j that are equal may appear in pairs, the feedback overheads can be further reduced.

In addition, the foregoing matrix A_(i) or matrix B_(i) may also use another form, which is not further elaborated herein.

It should be noted that, each of the foregoing matrices may further be multiplied by a scale factor, so as to implement power normalization or power balancing.

The sending unit 113 is configured to send a precoding matrix indicator PMI to the base station, where the PMI corresponds to the selected precoding matrix, so that the base station obtains the precoding matrix according to the PMI.

Specifically, the precoding matrix is included in a precoding matrix set or a codebook; and the PMI is used to indicate the selected precoding matrix in the precoding matrix set or the codebook.

Specifically, sending a precoding matrix indicator PMI to the base station includes: sending the precoding matrix indicator PMI to the base station, where the PMI may include only one specific value. In this case, the PMI directly indicates the precoding matrix W. For example, if there are a total of 16 different precoding matrices, PMI=0, . . . , 15 may be used to respectively indicate precoding matrices W whose labels are 0, 1, . . . , 15.

Specifically, sending a precoding matrix indicator PMI to the base station may also include: sending precoding matrix indicators PMI₁ and PMI₂ to the base station, where PMI₁ and PMI₂ are used to indicate the matrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B) in formula (2) and the matrix W₂, respectively; and in this case, the matrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B), and the matrix W₂ are respectively indicated by PMI₁ and PMI₂ in the codebook; or

sending precoding matrix indicators PMI₁₁, PMI₁₂, and PMI₂ to the base station, where PMI₁₁, PMI₁₂, and PMI₂ are used to indicate the matrix A_(i), 1≤i N_(B), the matrix B_(i), 1≤i≤N_(B), and the matrix W₂, respectively; and in this case, the matrix A_(i), 1≤i≤N_(B), the matrix B_(i), 1≤i≤N_(B), and the matrix W₂ are respectively indicated by PMI₁₁, PMI₁₂, and PMI₂ in the codebook.

Specifically, sending a precoding matrix indicator PMI to the base station may also include: sending precoding matrix indicators PMI_(1,i) 1≤i≤N_(B)/2 and PMI₂ to the base station, where PMI_(1,i), 1≤i≤N_(B)/2 and PMI₂ are used to indicate a matrix X_(2i−1)=X_(2i)=A_(2i)⊗B_(2i), 1≤i≤N_(B)/2 and the matrix W₂ respectively; and in this case, X_(2i−1)=X_(2i), and the matrices appear in pairs; or

sending precoding matrix indicators PMI_(11,i), PMI_(12,i), and PMI₂ to the base station, where PMI_(11,i), PMI_(12,i), and PMI₂ are used to indicate a matrix A_(2i−1)=A_(2i), 1≤i≤N_(B)/2, the matrix B_(2i−1)=B_(2i), 1≤i≤N_(B)/2, and the matrix W₂, respectively; and in this case, A_(2i−1)=A_(2i), B_(2i−1)=B_(2i), and the matrices appear in pairs.

Further, the precoding matrix indicators PMI₁ and PMI₂, or the precoding matrix indicators PMI₁₁, PMI₁₂, and PMI₂ have different time domain granularities or frequency domain granularities, for example, PMI₁ and PMI₂, or PMI₁₁, PMI₁₂, and PMI₂ separately indicate different periods or bandwidth channel features, or are obtained based on different subframe periods or subband sizes.

Alternatively, further, the precoding matrix indicators PMI₁₁ and PMI₁₂ are sent to the base station according to different time periods.

Specifically, sending a precoding matrix indicator PMI to the base station may also include: sending precoding matrix indicators PMI_(1,i), 1≤i≤N_(B) and PMI₂ to the base station, where PMI_(1,i), 1≤i≤N_(B) and PMI₂ are used to indicate the matrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B) and the matrix W₂, respectively; or

sending precoding matrix indicators PMI₁₁, PMI₁₂, and PMI₂ to the base station, where PMI_(11,i), PMI_(12,i), and PMI₂ are used to indicate the matrix A_(i), 1≤i≤N_(B), the matrix B_(i), 1≤i≤N_(B), and the matrix W₂, respectively.

Specifically, sending a precoding matrix indicator PMI to the base station may be sending, by the UE, the precoding matrix indicator PMI to the base station through a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH).

Further, sending a precoding matrix indicator PMI to the base station may be separately sending, by the UL by using different subframes or according to different periods, the foregoing PMI₁ and PMI₂; or PMI₁₁, PMI₁₂, and PMI₂; or PMI_(1,i), 1≤i≤N_(B), and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B), and PMI₂; or PMI_(1,i), 1≤i≤N_(B)/2, and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B)/2 and PMI₂ to the base station.

Further, sending a precoding matrix indicator PMI to the base station may also be separately sending, by the UE for different subbands or subband sizes in a frequency domain, the foregoing PMI₁ and PMI₂; or PMI₁₁, PMI₁₂, and PMI₂; or PMI_(1,i), 1≤i≤N_(B), and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B), and PMI₂; or PMI_(1,i), 1≤i≤N_(B)/2, and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B)/2 and PMI₂ to the base station.

In this embodiment of the present invention, a user equipment determines and sends a precoding matrix indicator PMI, where the PMI indicates a precoding matrix. The precoding matrix has a structure of W=W₁W₂, where W₁ is a block diagonal matrix in which each block matrix on a diagonal line is X_(i)=A_(i)⊗B_(i), and i=1, . . . , N_(B), where the matrix A_(i) or the matrix B_(i) effectively supports channel state information quantization in a horizontal direction or a vertical direction, respectively. This can fully use a degree of freedom of an active antenna system AAS in a horizontal direction and a vertical direction, thereby greatly improving channel state information feedback accuracy. In addition, multiple block matrices X_(i) may separately correspond to antenna groups of different polarizations or at different locations, so that the foregoing precoding matrix matches multiple antenna deployments or configurations. The foregoing codebook structure greatly improves performance of MIMO, and especially that of MU-MIMTO. Moreover, one or more PMIs are fed back based on a subset to indicate a precoding matrix, which fully uses time/frequency domain/spatial correlation of a channel, thereby greatly reducing feedback overheads.

FIG. 5 is a base station eNB 12 for determining a precoding matrix indicator according to an embodiment of the present invention. As shown in the figure, the base station eNB 12 includes: a sending unit 121 and a receiving unit 122.

The sending unit 121 is configured to send a reference signal to a user equipment UE.

Specifically, the reference signal may include a channel state information reference signal (CSI RS), a demodulation reference signal (demodulation RS, DM RS), or a cell-specific reference signal (cell-specific RS, CRS). Abase station eNB may notify the user equipment UE of a resource configuration of the reference signal by using RRC (Radio Resource Control) signaling or downlink control information (DC), and instruct the UE to obtain the reference signal from a corresponding resource or subframe. The user equipment UE may also implicitly obtain, based on other information such as a cell identity ID, the resource configuration of the reference signal, and obtain the reference signal from the corresponding resource or subframe. The receiving unit 122 is configured to receive a precoding matrix indicator PMI sent by the user equipment UE, where the PMI corresponds to a precoding matrix selected, based on the reference signal, from a codebook by the user equipment; and a precoding matrix W included in the codebook is a product of two matrices W₁ and W₂, and the precoding matrix W has the structure shown in formulas (1) to (4).

Specifically, each column of the matrix A_(i) or of the matrix B_(i) may be a DFT vector or may be a column vector of a Hadamard matrix, as shown in formulas (5) to (11); or

specifically, the matrix A_(i) or the matrix B_(i) may also be a precoding matrix in a 2-antenna codebook or a 4-antenna codebook of an LTE R8 system, or in an 8-antenna codebook of an LTE R10 system.

Further, the matrix W₂ is used to select or weight and combine a column vector in the matrix W₁, so as to form the matrix W.

In an example in which the number of block matrices is N_(B)=2 and there are 32 transmit antennas, matrices that form the precoding matrix W may separately be those shown in formulas (12) to (23); or B_(i) is a precoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

In an example in which the number of block matrices is N_(B)=2 and there are 32 transmit antennas, matrices that form the precoding matrix W may separately be those shown in formulas (24) to (30); or B_(i) is a precoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

Specifically, the precoding matrix selected, based on the reference signal, from a codebook includes: the precoding matrix selected, based on the reference signal, from a codebook subset, where

the codebook subset may be a codebook subset that is predefined; or a codebook subset that is reported by the UE to the base station eNB, determined by the base station eNB based on the report from the UE, and notified to the UE; or a codebook subset that is determined and reported by the UE, for example, a latest reported codebook subset.

Further, the codebook subset may include a subset of the matrix W₁, the matrix A_(i), the matrix B_(i), or the matrix W₂.

Further, the codebook subsets have a same subset of the matrix W₁, the matrix A_(i), the matrix B_(i), or the matrix W₂. In this way, the codebook subsets overlap each other, which can overcome an edge effect of channel state information quantization.

Further, in the precoding matrix, block matrices X_(i) and X_(j), i≈j may be unequal, or may also be equal. If there are multiple cases that X_(i) and X_(j), i≈j are equal, for example, X_(i) and X_(j), i≈j that are equal may appear in pairs, feedback overheads can be further reduced.

In addition, the foregoing matrix A_(i) or matrix B_(i) may also use another form, which is not further elaborated herein.

It should be noted that, each of the foregoing matrices may further be multiplied by a scale factor, so as to implement power normalization or power balancing.

Specifically, the precoding matrix is included in a precoding matrix set or a codebook; and the PMI is used to indicate the selected precoding matrix in the precoding matrix set or the codebook.

Specifically, receiving a precoding matrix indicator PMI sent by the user equipment UE includes: receiving the precoding matrix indicator PMI sent by the user equipment UE, where the PMI may include only one specific value. In this case, the PMI directly indicates the precoding matrix W. For example, if there are a total of 16 different precoding matrices, PMI=0, . . . , 15 may be used to respectively indicate precoding matrices W whose labels are 0, 1, . . . 15.

Specifically, receiving a precoding matrix indicator PMI sent by the user equipment UE may also include: receiving precoding matrix indicators PMI₁ and PMI₂ sent by the user equipment UE, where PMI₁ and PMI₂ are used to indicate the matrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B) in formula (2) and the matrix W₂, respectively; and in this case, the matrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B) and the matrix W₂ are respectively indicated by PMI₁ and PMI₂ in the codebook; or

receiving precoding matrix indicators PMI₁₁, PMI₁₂, and PMI₂ sent by the user equipment UE, where PMI₁₁, PMI₁₂, and PMI₂ are used to indicate the matrix A_(i), 1≤i≤N_(B), the matrix B_(i), 1≤i≤N_(B), and the matrix W₂, respectively; and in this case, the matrix A_(i), 1≤i≤N_(B), the matrix B_(i), 1≤i≤N_(B), and the matrix W₂ are respectively indicated by PMI₁₁, PMI₁₂, and PMI₂ in the codebook.

Further, the precoding matrix indicators PMI₁ and PMI₂, or the precoding matrix indicators PMI₁₁, PMI₁₂, and PMI₂ have different time domain granularities or frequency domain granularities, for example, PMI₁ and PMI₂, or PMI₁₁, PMI₁₂, and PMI₂ separately indicate different periods or bandwidth channel features, or are obtained based on different subframe periods or subband sizes.

Alternatively, further, the precoding matrix indicators PMI₁₁ and PMI₁₂ are sent to the base station according to different time periods.

Specifically, receiving a precoding matrix indicator PMI sent by the user equipment UE may also include: receiving precoding matrix indicators PMI_(1,i), 1≤i≤N_(B), and PMI₂ sent by the user equipment UE, where PMI_(1,i), 1≤i≤N_(B) and PMI₂ are used to indicate the matrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B) the matrix W₂, respectively; or

receiving precoding matrix indicators PMI_(11,i), PMI_(12,i), and PMI₂ sent by the user equipment UE, where PMI_(11,i), PMI_(12,i), and PMI₂ are used to indicate the matrix A_(i), 1≤i≤N_(B), the matrix B_(i), 1≤i≤N_(B), and the matrix W₂, respectively; or receiving precoding matrix indicators PMI_(1,i), 1≤i≤N_(B)/2, and PMI₂ sent by the user equipment UE, where PMI_(1,i), 1≤i≤N_(B)/2 and PMI₂ are used to indicate a matrix X_(2i−1)=X_(2i)=A_(2i)⊗B_(2i), 1≤i≤N_(B)/2, and the matrix W₂, respectively; and in this case, X_(2i−1)=X_(2i), and the matrices appear in pairs; or

receiving precoding matrix indicators PMI_(11,i), PMI_(12,i), and PMI₂ sent by the user equipment UE, where PMI_(11,i), PMI_(12,i), and PMI₂ are used to indicate a matrix A_(2i−1)=A_(2i), 1≤i≤N_(B)/2, the matrix B_(2i−1)=B_(2i), 1≤i≤N_(B)/2, and the matrix W₂, respectively; and in this case, A_(2i−1)=A_(2i), B_(2i−1)=B_(2i), and the matrices appear in pairs.

Specifically, receiving a precoding matrix indicator PMI sent by the user equipment UE may be receiving, through a physical uplink control channel (PUCCI) or a physical uplink shared channel (PUSCH), the precoding matrix indicator PMI sent by the user equipment UE.

Further, receiving a precoding matrix indicator PMI sent by the user equipment UE may be separately receiving, by the base station by using different subframes or according to different periods, the foregoing precoding matrix indicators sent by the user equipment UE, which are PMI₁ and PMI₂; or PMI₁₁, PMI₁₂, and PMI₂; or PMI_(1,i), 1≤i≤N_(B) and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B), and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B)/2, and PMI₂; or

may also be receiving the foregoing PMI₁ and PMI₂; or PMI₁₁ PMI₁₂, and PMI₂; or PMI_(1,i), 1≤i≤N_(B) and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B), and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B)/2, and PMI that are sent for different subbands or subband sizes in a frequency domain by the user equipment UE.

In this embodiment of the present invention, the base station eNB receives a precoding matrix indicator PMI sent by the user equipment UE, where the PMI indicates a precoding matrix. The precoding matrix has a structure of W=W₁W₂, where W₁ is a block diagonal matrix in which each block matrix on a diagonal line is X_(i)=A_(i)⊗B_(i), and i=1, . . . , N_(B), where the matrix A_(i) or the matrix B_(i) effectively supports channel state information quantization in a horizontal direction or a vertical direction, respectively. This can fully use a degree of freedom of an active antenna system AAS in a horizontal direction and a vertical direction, thereby greatly improving CSI feedback accuracy. In addition, multiple block matrices X_(i) may separately correspond to antenna groups of different polarizations or at different locations, so that the foregoing precoding matrix matches multiple antenna deployments or configurations. The foregoing codebook structure greatly improves performance of MIMO, and especially that of MU-MIMO. Moreover, one or more PMIs are fed back based on a subset to indicate a precoding matrix, which fully uses time/frequency domain/spatial correlation of a channel, thereby greatly reducing feedback overheads.

A person skilled in the art may be further aware that, in combination with the examples described in the embodiments disclosed in this specification, units and algorithm steps may be implemented by electronic hardware, computer software, or a combination thereof. To clearly describe the interchangeability between the hardware and the software, the foregoing has generally described structures and steps of each example according to functions. Whether the functions are performed by hardware or software depends on particular applications and design constraint conditions of the technical solutions. A person skilled in the art may use different methods to implement the described functions for each particular application, but it should not be considered that the implementation goes beyond the scope of the present invention.

In combination with the embodiments disclosed in this specification, method or algorithm steps may be implemented by hardware, a software module executed by a processor, or a combination thereof. The software module may reside in a random access memory (RAM), memory, a read-only memory (ROM), an electrically programmable ROM, an electrically erasable programmable ROM, a register, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.

The foregoing specific embodiments further describe the objectives, technical solutions, and beneficial effects of the present invention in detail. It should be understood that the foregoing descriptions are merely specific embodiments of the present invention, but are not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, or improvement made without departing from the spirit and principle of the present invention should fall within the protection scope of the present invention. 

What is claimed is:
 1. A method for determining a precoding matrix indicator, the method comprising: sending, by a base station, a reference signal to a terminal device; and receiving, by the base station, a precoding matrix indicator (PMI) from the terminal device, wherein the PMI corresponds to a precoding matrix in a codebook, wherein each precoding matrix W comprised in the codebook is a product of two matrices W₁ and W₂, W=W₁W₂, wherein the matrix W₁ is a block diagonal matrix, W₁=diag{X₁, . . . , X_(N) _(B) }, N_(B)>1, each block matrix X_(i) being a Kronecker product of a matrix A_(i) and a matrix B_(i), X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B), wherein the matrix A_(i) and the matrix B_(i) are for channel state information quantization in two degrees of freedom of an antenna array respectively.
 2. The method according to claim 1, wherein each column of the matrix A_(i) and the matrix B_(i) is a discrete Fourier transform (DFT) vector, and the two degrees of freedom of the antenna array comprise a degree of freedom in a horizontal direction and a degree of freedom in a vertical direction.
 3. The method according to claim 1, wherein receiving by the base station the PMI from the terminal device comprises: receiving a third precoding matrix indicator PMI₁₁, a fourth precoding matrix indicator PMI₁₂, and a fifth precoding matrix indicator PMI₂ from the terminal device, wherein the third precoding matrix indicator PMI₁₁ is used to indicate the matrix A_(i), wherein 1≤i≤N_(B); the fourth precoding matrix indicator PMI₁₂ is used to indicate the matrix B_(i), wherein 1≤i≤N_(B), and the fifth precoding matrix indicator PMI₂ is used to indicate the matrix W₂.
 4. The method according to claim 1, wherein block matrices in the matrix W₁ satisfy X_(2j−1)=X_(2j), 1≤j≤N_(B)/2.
 5. The method according to claim 1, wherein the matrix W₂ is used to select or weight and combine at least one column vector in the matrix W₁ to form the matrix W.
 6. The method according to claim 1, wherein the codebook comprises a codebook subset consisting of precoding matrices corresponding to a subset of the matrix A_(i) and the matrix B_(i).
 7. The method according to claim 6, further comprises: notifying, by the base station, the subset of the matrix A_(i) and the matrix B_(i) to the terminal device.
 8. A device, comprising: a transmitter configured to send a reference signal to a terminal device; and a receiver configured to receive a precoding matrix indicator (PMI) from the terminal device, wherein the PMI corresponds to a precoding matrix in a codebook, wherein each precoding matrix W comprised in the codebook is a product of two matrices W₁ and W₂, W=W₁W₂, wherein the matrix W₁ is a block diagonal matrix, W₁=diag{X₁, . . . , X_(N) _(B) }, N_(B)>1, each block matrix X_(i) being a Kronecker product of a matrix A_(i) and a matrix B_(i), X_(i)=A_(i) ⊗B_(i), 1≤i≤N_(B), wherein the matrix A_(i) and the matrix B_(i) are for channel state information quantization in two degrees of freedom of an antenna array respectively.
 9. The device according to claim 8, wherein each column of the matrix A_(i) and the matrix B_(i) is a discrete Fourier transform (DFT) vector, and the two degrees of freedom of the antenna array comprise a degree of freedom in a horizontal direction and a degree of freedom in a vertical direction.
 10. The device according to claim 8, wherein receiving the PMI from the terminal device comprises: receiving a third precoding matrix indicator PMI₁₁, a fourth precoding matrix indicator PMI₁₂, and a fifth precoding matrix indicator PMI₂ from the terminal device, wherein the third precoding matrix indicator PMI₁₁ is used to indicate the matrix A_(i), wherein 1≤i≤N_(B); the fourth precoding matrix indicator PMI₁₂ is used to indicate the matrix B_(i), wherein 1≤i≤N_(B), and the fifth precoding matrix indicator PMI₂ is used to indicate the matrix W₂.
 11. The device according to claim 8, wherein block matrices in the matrix W₁ satisfy X_(2j−1)=X_(2j), 1≤j≤N_(B)/2.
 12. The device according to claim 8, wherein the matrix W₂ is used to select or weight and combine at least one column vector in the matrix W₁ to form the matrix W.
 13. The device according to claim 8 wherein the codebook comprises a codebook subset consisting of precoding matrices corresponding to a subset of the matrix A_(i) and the matrix B_(i).
 14. The device according to claim 13, the transmitter is configured to notify the subset of the matrix A_(i) and the matrix B_(i) to the terminal device.
 15. A non-transitory computer-readable storage medium storing instructions which, when executed by at least one processor in a base station, cause the base station to: send a reference signal to a terminal device; and receive a precoding matrix indicator (PMI) from the terminal device, wherein the PMI corresponds to a precoding matrix in a codebook, wherein each precoding matrix W comprised in the codebook is a product of two matrices W₁ and W₂, W=W₁W₂, wherein the matrix WV is a block diagonal matrix, W₁=diag {X₁, . . . , X_(N) _(B) }, N_(B)>1, each block matrix X_(i) being a Kronecker product of a matrix A_(i) and a matrix B_(i), X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B), wherein the matrix A_(i) and the matrix B_(i) are for channel state information quantization in two degrees of freedom of an antenna array respectively.
 16. The non-transitory computer-readable storage medium according to claim 15, wherein each column of the matrix A_(i) and the matrix B_(i) is a discrete Fourier transform (DFT) vector, and the two degrees of freedom of the antenna array comprise a degree of freedom in a horizontal direction and a degree of freedom in a vertical direction.
 17. The non-transitory computer-readable storage medium according to claim 15, wherein receiving the PMI from the terminal device comprises: receiving a third precoding matrix indicator PMI₁₁, a fourth precoding matrix indicator PMI₁₂, and a fifth precoding matrix indicator PMI₂ from the terminal device, wherein the third precoding matrix indicator PMI₁₁ is used to indicate the matrix A_(i), wherein 1≤i≤N_(B); the fourth precoding matrix indicator PMI₁₂ is used to indicate the matrix B_(i) wherein 1≤i≤N_(B), and the fifth precoding matrix indicator PMI₂ is used to indicate the matrix W₂.
 18. The non-transitory computer-readable storage medium according to claim 15, wherein block matrices in the matrix W₁ satisfy X_(2j−1)=X_(2j), 1≤j≤N_(B)/2.
 19. The non-transitory computer-readable storage medium according to claim 15, wherein the matrix W₂ is used to select or weight and combine at least one column vector in the matrix W₁ to form the matrix W.
 20. The non-transitory computer-readable storage medium according to claim 15, wherein the codebook comprises a codebook subset consisting of precoding matrices corresponding to a subset of the matrix A_(i) and the matrix B_(i).
 21. The non-transitory computer-readable storage medium according to claim 20, wherein the instructions which, when executed by at least one processor in the base station, cause the base station to notify the subset of the matrix A_(i) and the matrix B_(i) to the terminal device.
 22. A communications device, comprising: at least one processor; and a memory configured to store computer operation instructions that, when executed by the at least one processor, cause the at least one processor to perform: sending a reference signal to a terminal device; and receiving a precoding matrix indicator (PMI) from the terminal device, wherein the PMI corresponds to a precoding matrix in a codebook, wherein each precoding matrix W comprised in the codebook is a product of two matrices W₁ and W₂, W=W₁W₂, wherein the matrix WV is a block diagonal matrix, W₁=diag{X₁, . . . , X_(N) _(B) }N_(B)>1 each block matrix X_(i) being a Kronecker product of a matrix A_(i) and a matrix B_(i), X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B), wherein the matrix A_(i) and the matrix B_(i) are for channel state information quantization in two degrees of freedom of an antenna array respectively.
 23. The communications device according to claim 22, wherein each column of the matrix A_(i) and the matrix B_(i) is a discrete Fourier transform (DFT) vector, and the two degrees of freedom of the antenna array comprise a degree of freedom in a horizontal direction and a degree of freedom in a vertical direction.
 24. The communications device according to claim 22, wherein receiving the PMI from the terminal device comprises: receiving a third precoding matrix indicator PMI₁₁, a fourth precoding matrix indicator PMI₁₂, and a fifth precoding matrix indicator PMI₂ from the terminal device, wherein the third precoding matrix indicator PMI₁₁ is used to indicate the matrix A_(i), wherein 1≤i≤N_(B); the fourth precoding matrix indicator PMI₁₂ is used to indicate the matrix B_(i) wherein 1≤i≤N_(B), and the fifth precoding matrix indicator PMI₂ is used to indicate the matrix W₂.
 25. The communications device according to claim 22, wherein block matrices in the matrix W₁ satisfy X_(2j−1)=X_(2j), 1≤j≤N_(B)/2.
 26. The communications device according to claim 22, wherein the matrix W₂ is used to select or weight and combine at least one column vector in the matrix W₁ to form the matrix W.
 27. The communications device according to claim 22, wherein the codebook comprises a codebook subset consisting of precoding matrices corresponding to a subset of the matrix A_(i) and the matrix B_(i).
 28. The communications device according to claim 27, the at least one processor is further caused to perform: notifying the subset of the matrix A_(i) and the matrix B_(i) to the terminal device. 